Why does my cat have thumb-like toes?

Q:I recently found two abandoned kittens. The female is calico and has normal front paws. The male is a red tabby with four toes on his front paws and one thumb-like toe that actually looks like two toes that didn’t separate. I have never seen this before and I have had a considerable number of cats. Someone told me that this paw formation is characteristic of some breed. Is that the case or is this just a deformation not related to breed? If not, have you seen what I described in other cats?

A: What you’re describing is polydactylism. Polydactyly (from the Greek: poly = many, daktulos = fingers) is a common trait among cats. It is a naturally occurring genetic variation that occurs in many animals as well as in humans. The lore behind polydactyl cats is intriguing. It is believed that English Puritans may have taken polydactyl cats on their ships to Boston during the mid-1600s, although it is also possible that the mutation developed in cats already residing in the Boston area. The offspring of these cats are believed to have then traveled on trading ships from Boston to Yarmouth, Mass., and Halifax, Nova Scotia, which might explain why these areas have a higher than normal incidence of polydactyly.

Polydactyl cats are occasionally referred to as “mitten cats,” “thumb cats,” and “Hemingway cats,” the latter name referring to the writer Ernest Hemingway, who made his home on the small island of Key West, Fla. Hemingway shared the island with almost 50 cats, including a six-toed polydactyl given to him by a ship captain. For the next 100 years, unrestrained breeding between this cat’s descendents and the local cats (alas, they weren’t as keen on spaying and neutering as we are today) led to a high percentage (almost 50%!) of polydactyls in the local population.

Historically, the original unregistered Maine Coon cats had a high incidence of polydactylism—around 40%! Breed standards required a normal foot configuration, and did not allow polydactyly in Maine Coons, and so the trait was deliberately bred out of this breed. In the Netherlands and Belgium, there is currently a move to restore the polydactyl form of the breed.

Polydactylism doesn’t affect cats adversely. It offers them no advantages, nor does it yield any disadvantages. (If it did, polydactyl cats would have likely died out fairly quickly.) It is simply an enchanting quirk. It is an anomaly—a deviation from the norm—rather than a deformity. While people often worry about cats catching the extra toes on furnishings, this is rarely a problem. The toenails associated with the extra toes tend to be normal nails, although occasionally, the extra toe is incompletely formed, and the nail bed is deformed, leading to claw problems such as ingrown or overgrown claws. Like all kitty toenails, the extra ones require regular trimming.